As widely known in the art, slaughtering of birds such as chicken and similar is an in-line process. In bird slaughtering equipments, a suspended line in closed circuit is designed and provided with a series of hooks to support the birds, which travel under speed which is pre-determined by the line. In a first loading station, birds are tied to said hooks by their feet and therefore move through the line upside down. In a second station, the birds are submitted to a step called stunning. In that step, the bird's head, supported by the line hook, is immersed into a tub containing an electricity-conducting liquid. As the head of the bird enters the tub, the bird closes an electric circuit where the poles are the hook/line and the electricity conducting liquid/tub, and the bird is therefore stunned by means of controlled shock. Upon stunning the bird, the continued movement of the line transports the stunned bird to a slaughtering station as properly stated, where the bird is slaughtered by decollation, and to a bleeding station designed to take off as much blood as possible from the slaughtered and decollated bird. Therefore, the bird may be unloaded or submitted to complementary steps according to the type of equipment at issue. Anyway, free line hooks are again transported to the bird loading station to upload a new bird and thus restart the working cycle. A few references to bird slaughtering line stations may be found in patents GB 1,123,300 dated May 10, 1966; GB 1,188,869 dated Apr. 22, 1970; U.S. Pat. No. 3,828,397 dated Aug. 13, 1974; U.S. Pat. No. 4,751,767 dated Jun. 21, 1988; as well as in the publication WO 97/01284 published on Jan. 16, 1997.
The size of the line, in terms of length, the quantity of hooks held by the line and the speed of displacement of said hooks through the line circuit are inherent characteristics to each equipment and, as a function of said characteristics, a maximum capacity of bird slaughtering may be established for each equipment. Said maximum slaughtering ability, however, is limited by a number of operational factors, among which we should highlight that a hook frequently travels empty through the circuit for being not possible to fill it at the loading station. This happens because the birds, in this step of the process, are alive and do not move according to any programmable behavior model.
For the slaughtering and bleeding steps, the lack of a bird in a hook does not bring in huge inconveniences, aside from the mere productivity reduction. In the stunning step, however, this problem may be much more relevant.
As known, the fixed tub has a given length over the direction of hook displacement by the line and thus may receive a given quantity of birds, which may be calculated by the ratio between the length of the tub and the distance between each hook in the line. To apply the stunning current to birds inside the tub (specifically with the head inside the tub and tied by their feet to the hooks on the line), the line is connected to a first pole of a stunning device, while the tub containing a conducting liquid (e.g. pure water or saline solution, among others) is connected to a second pole of said stunning device. The stunning device keeps a potential difference between the tub and the line, so that each bird inside the tub is submitted to the passage of stunning current. The efficient stunning of each bird is an essential requirement for consecutive steps (slaughtering and bleeding) to be successfully performed.
As known by the experts in the art, efficient stunning of birds is directly related to better quality and higher productivity of processed meat. As an example, if the stunning current is not appropriate, hematomas may be formed, mainly on the bird chest region, by disrupting vessels and bones, increasing loss in the quantity of produced meat. Furthermore, stunning influences bird relaxing conditions (including contraction or distension of birds' arteries and capillaries), among others, and therefore influences the grade of bird bleeding after slaughtering. On the other hand, it is also known that the lower the quantity of residual blood in the bird, the better the quality of produced meat. For better reference to the bleeding step, please refer to the U.S. Pat. No. 5,954,573 dated Sep. 21, 1999.
In this sense, the state of the art forecasts a number of stunning devices or devices to control the type of current to be applied to birds during stunning. Therefore, these devices supply currents presenting alternated sinusoidal, square, saw-toothed etc. or continued waves, so to improve stunning. According to the most recent skills, birds should be stunned by means of electrical discharges under low tension and with high frequency. References concerning the forms of current being employed to stun birds may be obtained from the following documents: U.S. Pat. No. 3,474,490 dated Sep. 18, 1968; NL 1,006,091 published on Nov. 25, 1998; and NL 1,007,271, published on Apr. 19, 1999. Furthermore, the document FR 2,610,163 dated Jul. 29, 1988 discloses stunning by means of continued current.
Furthermore, and specifically when birds are slaughtered bearing in mind their purchase by specific ethnic/religious groups, various standards should be followed for the meat to be consumed. In these cases, slaughtering is supervised by a religious representative who should confirm that meat processing conditions have followed imposed patterns. It is not rare that said standards impose stunning current/tension conditions not compatible to efficiently stun a bird. Furthermore, the imposition of maximum or minimum current, or within a pre-determined range, may be complex due to the currently available equipment in the market.
Finally, and also as known by the experts in this field, permeability to the passage of an electric current or, inversely, birds' electric resistance varies according to their condition. Therefore, a group of birds may have different electric resistance from other groups as a function of the humidity of the bird (resulting from previous bird washing), feeding, quantity of ingested liquids, size of the bird, bird species, etc. Therefore, the control of the stunning current may be very difficult as a function of variations found from bird to bird.
Furthermore, and despite all regulations in this field being in terms of the characteristics of the stunning current, systems currently available in the market do not include automatic means to efficiently control the stunning current for each bird.
A system, method and device intended to efficiently control the slaughtering current of each bird within a device for bird slaughtering is therefore required.